At least nine private security guards at Kennedy Airport have been fired this year for sleeping on the job, The Post has learned.

But the supervisor responsible for getting many of them sacked is still on the job — even though he, too, was caught snoozing, the employees say.

The incidents came to light because several of the dismissed guards filed union grievances after evening supervisor Ronald Denig and at least one other boss snapped incriminating pictures of them catching zzzz’s while on duty.

The guards earn a minimum of $16.99 an hour working for Covenant Aviation Security, a Port Authority contractor.

Denig and other supervisors make about $10 an hour more.

In addition to the nine guards, others may also have been sacked, but it’s unclear how many because some went quietly, without protesting to their union.

One source said as many as 10 additional guards have been given pink slips for similar offenses in the last two months alone.

About 300 guards are stationed at JFK.

A picture of Denig allegedly snoozing was taken by a colleague of the dismissed guards — who sneaked up on him while he was sleeping in a company car, parked in a deserted lot, multiple sources said.

It was the kind of revenge angry guards had dreamed about — but they soon got a rude awakening.

That’s because Denig’s on-the-job siesta earned the equivalent of a big yawn from his bosses, who hit him with only a five-day suspension.

“These guards are the first line of defense at the airport,” said a PA police official.

“Obviously, if they’re sleeping, it’s something that cannot be tolerated.”

The guards’ duties include patrolling near tarmacs, examining vehicles that pass through sensitive areas, checking unoccupied buildings, and examining airport employees to make sure they have proper ID, sources say.

Another PA official insisted the agency has not fallen asleep at the switch.

“Security is a top priority and we employ a multilayered security protocol and anything less than absolute adherence is not tolerated,” the official said.

Phone calls to Covenant were not returned.

Denig did not return a message left at his home.

Matt Nerzig, a spokesman for the guards’ union, Local 32BJ, Service Employees International, lashed out at the disparity in punishment.

“The workers have every right to be disgruntled at Covenant’s handling of many issues, including this one, which shows a troubling double standard that should not be tolerated,” Nerzig said.

Covenant is on the way out — but not because of the snooze scandal.

FJC Security, which had been providing guards for Newark Airport, offered a lower bid to do the job at La Guardia and JFK for four years starting in February.